Abstract: A total of 21 different disease-grading summer maize groups were formed by fixed-point natural infection of maize brown spot in the field, and mass
loss estimation models of single ear mass and 100-grain mass were constructed by stepwise regression with DPS software. The mass loss estimation models of single ear and 100-grain were Y=-4.012+0.377X₁-0.228X₂+0.694X₃-0.144X₄ and Y=-4.536+0.173X₁+0.188X₂+0.248X₃-0.034X₄, respectively, where Y was yield loss rate, X₁ was the disease index at flowering stage, X₂ was the disease index at pollination stage, X₃ was the disease index at filling stage, and X₄ was the disease index at dough stage. The measured relationships between the disease indices at differen
t growth stages and the mass loss for single ear and 100-grain coincided well with the modeling results. Maize brown spot directly affected the net photosynthetic rate of ear height leaf and the activities of RuBP carboxylase and PEP carboxylase. The higher the disease-grade, the lower the net photosynthetic rate and the activities of the two enzymes were.

Key words: maize brown spot (Physoderma maydis), yield loss, model construction, photosynthesis rate, photosynthetic carboxylase